Target supply device

ABSTRACT

A target supply device includes a nozzle portion, a cover, a first electrode, and a potential controller. The nozzle portion has a through-hole defined therein to allow a target material to be discharged therethrough. The cover includes an electrically conductive material and is disposed to cover the nozzle portion. The cover has a through-hole defined therein to allow the target material to pass therethrough. The first electrode is disposed on the cover. The first electrode has a through-hole to allow the target material to pass therethrough. The potential controller is configured to control the first electrode to have a first potential that is lower than a second potential of the cover.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2012-012955 filed Jan. 25, 2012.

BACKGROUND

1. Technical Field

The present disclosure relates to a target supply device.

2. Related Art

In recent years, semiconductor production processes have become capable of producing semiconductor devices with increasingly fine feature sizes, as photolithography has been making rapid progress toward finer fabrication. In the next generation of semiconductor production processes, microfabrication with feature sizes at 60 nm to 45 nm, and further, microfabrication with feature sizes of 32 nm or less will be required. In order to meet the demand for microfabrication with feature sizes of 32 nm or less, for example, an exposure apparatus is needed in which a system for generating EUV light at a wavelength of approximately 13 nm is combined with a reduced projection reflective optical system.

Three kinds of systems for generating EUV light are known in general, which include a Laser Produced Plasma (LPP) type system in which plasma is generated by irradiating a target material with a laser beam, a Discharge Produced Plasma (DPP) type system in which plasma is generated by electric discharge, and a Synchrotron Radiation (SR) type system in which orbital radiation is used to generate plasma.

SUMMARY

A target supply device according to one aspect of the present disclosure may include a nozzle portion, a cover, a first electrode and a potential controller. The nozzle portion has a through-hole defined therein to allow a target material to be discharged therethrough. The cover includes an electrically conductive material and is disposed to cover the nozzle portion. The cover has a through-hole defined therein to allow the target material to pass therethrough. The first electrode is disposed on the cover. The first electrode has a through-hole to allow the target material to pass therethrough. The potential controller is configured to control the first electrode to have a first potential that is lower than a second potential of the cover.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, selected embodiments of the present disclosure will be described with reference to the accompanying drawings.

FIG. 1 schematically illustrates an exemplary configuration of an LPP-type EUV light generation system.

FIG. 2 is a partial sectional view illustrating an exemplary configuration of an EUV light generation system including a target supply device according to a first embodiment of the present disclosure.

FIG. 3 is a partial sectional view illustrating the target supply device shown in FIG. 2 and peripheral components thereof.

FIG. 4A is a diagram showing an example of potentials that may be applied in a target supply device.

FIG. 4B is a diagram showing an example of potentials to be applied to various components in a target supply device according to the first embodiment.

FIG. 4C is a graph showing an amount of change in potentials of a target material and a shield electrode after plasma generation with respect to a potential of the shield electrode.

FIG. 5A is a plan view illustrating an example of a shield electrode used in a target supply device according to the first embodiment.

FIG. 5B is a sectional view illustrating the shield electrode shown in FIG. 5A being attached to a cover.

FIG. 6A is a plan view illustrating another example of a shield electrode used in a target supply device according to the first embodiment.

FIG. 6B is a sectional view illustrating the shield electrode shown in FIG. 6A being attached to a cover.

FIG. 7 is a partial sectional view illustrating a target supply device according to a second embodiment of the present disclosure and peripheral components thereof.

FIG. 8 is a partial sectional view illustrating a target supply device according to a third embodiment of the present disclosure and peripheral components thereof.

FIG. 9 is a diagram for describing a method for controlling a direction of a target using deflection electrodes.

FIG. 10 is a partial sectional view illustrating an exemplary configuration of an EUV light generation system including a target supply device according to a fourth embodiment of the present disclosure.

FIG. 11 is a diagram showing an example of potentials to be applied to various components in a target supply device according to the fourth embodiment.

FIG. 12 is a sectional view illustrating a part of a target supply device according to a fifth embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, selected embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiments to be described below are merely illustrative in nature and do not limit the scope of the present disclosure. Further, the configuration(s) and operation(s) described in each embodiment are not all essential in implementing the present disclosure. Note that like elements are referenced by like reference numerals and characters, and duplicate descriptions thereof will be omitted herein.

CONTENTS

-   1. Overview -   2. Overview of EUV Light Generation System -   2.1 Configuration -   2.2 Operation -   3. Target Supply Device Including Shield Electrode -   3.1 Configuration -   3.2 Operation -   3.3 Examples of Shield Electrode -   4. Target Supply Device Including Acceleration Electrode -   5. Target Supply Device Including Cover for Shielding Reservoir -   5.1 Configuration -   5.2 Operation -   6. Target Supply Device Where Pulse Voltage Is Applied to Shield     Electrode 7. Variations of Target Supply Device

1. Overview

In an LPP type EUV light generation apparatus, a target supply device may supply a target material toward a plasma generation region inside a chamber. The target material may then be irradiated with a pulse laser beam when the target material reaches the plasma generation region. Hence, the target material may be turned into plasma, and EUV light may be emitted from the plasma.

However, plasma that emits EUV light may include charged particles, such as electrons and ions of the target material. If the charged particles reach a nozzle of the target supply device, or the vicinity thereof, a target material may not be supplied stably to the plasma generation region.

According to one embodiment of the present disclosure, a target supply device may include a cover for a nozzle of the target supply device. The cover may have a through-hole formed therein to allow a target material to pass therethrough. The target supply device may also include an electrode having a through-hole formed therein to allow the target material to pass therethrough. A potential of the stated electrode may be controlled to a potential that is lower than a potential of the cover. Thus, charged particles may be prevented from reaching the nozzle of the target supply device, or the vicinity thereof. As a result, the target material may be supplied stably to the plasma generation region.

2. Overview of EUV Light Generation System 2.1 Configuration

FIG. 1 schematically illustrates an exemplary configuration of an LPP type EUV light generation system. An EUV light generation apparatus 1 may be used with at least one laser apparatus 3. Hereinafter, a system that includes the EUV light generation apparatus 1 and the laser apparatus 3 may be referred to as an EUV light generation system 11. As shown in FIG. 1 and described in detail below, the EUV light generation system 11 may include a chamber 2 and a target supply device 26. The chamber 2 may be sealed airtight. The target supply device 26 may be mounted onto the chamber 2, for example, to penetrate a wall of the chamber 2. A target material to be supplied by the target supply device 26 may include, but is not limited to, tin, terbium, gadolinium, lithium, xenon, or any combination thereof.

The chamber 2 may have at least one through-hole or opening formed in its wall, and a pulse laser beam 32 may travel through the through-hole/opening into the chamber 2. Alternatively, the chamber 2 may have a window 21, through which the pulse laser beam 32 may travel into the chamber 2. An EUV collector mirror 23 having a spheroidal surface may, for example, be provided in the chamber 2. The EUV collector mirror 23 may have a multi-layered reflective film formed on the spheroidal surface thereof. The reflective film may include a molybdenum layer and a silicon layer, which are alternately laminated. The EUV collector mirror 23 may have a first focus and a second focus, and may be positioned such that the first focus lies in a plasma generation region 25 and the second focus lies in an intermediate focus (IF) region 292 defined by the specifications of an external apparatus, such as an exposure apparatus 6. The EUV collector mirror 23 may have a through-hole 24 formed at the center thereof so that a pulse laser beam 33 may travel through the through-hole 24 toward the plasma generation region 25.

The EUV light generation system 11 may further include an EUV light generation controller 5 and a target sensor 4. The target sensor 4 may have an imaging function and detect at least one of the presence, trajectory, position, and speed of a target 27.

Further, the EUV light generation system 11 may include a connection part 29 for allowing the interior of the chamber 2 to be in communication with the interior of the exposure apparatus 6. A wall 291 having an aperture may be provided in the connection part 29. The wall 291 may be positioned such that the second focus of the EUV collector mirror 23 lies in the aperture formed in the wall 291.

The EUV light generation system 11 may also include a laser beam direction control unit 34, a laser beam focusing mirror 22, and a target collector 28 for collecting targets 27. The laser beam direction control unit 34 may include an optical element (not separately shown) for defining the direction into which the pulse laser beam 32 travels and an actuator (not separately shown) for adjusting the position and the orientation or posture of the optical element.

2.2 Operation

With continued reference to FIG. 1, a pulse laser beam 31 outputted from the laser apparatus 3 may pass through the laser beam direction control unit 34 and be outputted therefrom as the pulse laser beam 32 after having its direction optionally adjusted. The pulse laser beam 32 may travel through the window 21 and enter the chamber 2. The pulse laser beam 32 may travel inside the chamber 2 along at least one beam path from the laser apparatus 3, be reflected by the laser beam focusing mirror 22, and strike at least one target 27 as a pulse laser beam 33.

The target supply device 26 may be configured to output the target(s) 27 toward the plasma generation region 25 in the chamber 2. The target 27 may be irradiated with at least one pulse of the pulse laser beam 33. Upon being irradiated with the pulse laser beam 33, the target 27 may be turned into plasma, and rays of light 251 including EUV light may be emitted from the plasma. At least the EUV light included in the light 251 may be reflected selectively by the EUV collector mirror 23. EUV light 252, which is the light reflected by the EUV collector mirror 23, may travel through the intermediate focus region 292 and be outputted to the exposure apparatus 6. Here, the target 27 may be irradiated with multiple pulses included in the pulse laser beam 33.

The EUV light generation controller 5 may be configured to integrally control the EUV light generation system 11. The EUV light generation controller 5 may be configured to process image data of the target 27 captured by the target sensor 4. Further, the EUV light generation controller 5 may be configured to control at least one of: the timing when the target 27 is outputted and the direction into which the target 27 is outputted. Furthermore, the EUV light generation controller 5 may be configured to control at least one of: the timing when the laser apparatus 3 oscillates, the direction in which the pulse laser beam 31 travels, and the position at which the pulse laser beam 33 is focused. It will be appreciated that the various controls mentioned above are merely examples, and other controls may be added as necessary.

3. Target Supply Device Including Shield Electrode 3.1 Configuration

FIG. 2 is a partial sectional view illustrating an exemplary configuration of an EUV light generation system including a target supply device according to a first embodiment of the present disclosure. FIG. 3 is a sectional view illustrating the target supply device shown in FIG. 2 and peripheral components thereof. As shown in FIG. 2, a laser beam focusing optical system 22 a, the EUV collector mirror 23, the target collector 28, an EUV collector mirror mount 41, plates 42 and 43, a beam dump 44, and a beam dump support member 45 may be provided inside the chamber 2.

The chamber 2 may include an electrically conductive member formed of an electrically conductive material, such as metal. The chamber 2 may further include an electrically non-conductive member. In that case, the wall of the chamber 2 may, for example, be formed of an electrically conductive member, and electrically non-conductive members may be provided inside the chamber 2.

The plate 42 may be fixed to the chamber 2, and the plate 43 may be fixed to the plate 42. The EUV collector mirror 23 may be attached to the plate 42 through the EUV collector mirror mount 41.

The laser beam focusing optical system 22 a may include an off-axis paraboloidal mirror 221, a flat mirror 222, and holders 223 and 224 for the mirrors 221 and 222, respectively. The off-axis paraboloidal mirror 221 and the flat mirror 222 may be positioned on the plate 43 through the mirror holders 223 and 224, respectively, such that a pulse laser beam reflected sequentially by the mirrors 221 and 222 is focused in the plasma generation region 25.

The beam dump 44 may be fixed to the chamber 2 through the beam dump support member 45 to be positioned in an extension of a beam path of a pulse laser beam reflected by the flat mirror 222. The target collector 28 may be provided in an extension of a designed trajectory of the target 27.

The target supply device 26 may be mounted to the chamber 2. The target supply device 26 may include a reservoir 61, a target controller 52, a pressure adjuster 53, an inert gas cylinder 54, a DC power supply 55, a pulse voltage power supply 58, and a DC power supply 59.

The reservoir 61 may be configured to store a target material in a molten state. The reservoir 61 may be formed of a material that is not susceptible to reacting with a target material. For example, when tin is used as a target material, the reservoir 61 may be formed of at least one of molybdenum (Mo), tungsten (W), quartz (SiO₂), and silicon carbide (SiC). A heater (not separately shown) and a heater power supply (not separately shown) may further be provided to heat the reservoir 61. The reservoir 61 may be electrically insulated from the wall of the chamber 2.

As shown in FIG. 3, the target supply device 26 may further include a nozzle plate 62, an electrically insulating member 65, a pull-out electrode 66, a cover 67, and a shield electrode 68. The nozzle plate 62 may be fixed to an output end of the reservoir 61. The nozzle plate 62 may have a through-hole formed therein to allow a liquid target material to pass therethrough. Further, the nozzle plate 62 may have a protrusion 62 b, such that the aforementioned through-hole in the nozzle plate 62 may open at the protrusion 62 b.

The electrically insulating member 65 may be cylindrical in shape and be fixed to the reservoir 61 such that the electrically insulating member 65 covers a part of an output end of the reservoir 61. The electrically insulating member 65 may hold the nozzle plate 62 and the pull-out electrode 66 therein. The electrically insulating member 65 may provide electrical insulation between the nozzle plate 62 and the pull-out electrode 66. The pull-out electrode 66 may be provided to face a surface of the nozzle plate 62 on which the protrusion 62 b is formed. The pull-out electrode 66 may have a through-hole 66 a formed therein to allow targets 27 to pass therethrough.

A through-hole may be formed in the wall of the chamber 2, such that a flange 84 may be fixed to cover the through-hole in the chamber 2. A through-hole may be formed in the flange 84. The target supply device 26 may be fixed to the flange 84 such that the reservoir 61 passes through the through-hole in the flange 84. The flange 84 may be formed of an electrically non-conductive material.

The cover 67 may be attached to the flange 84 to cover a part of the target supply device 26 including at least the electrically insulating member 65. The cover 67 may further cover a part of the reservoir 61, the nozzle plate 62, and the pull-out electrode 66. The cover 67 may have a through-hole 67 a formed therein to allow targets 27 to pass therethrough.

The cover 67 may be formed of an electrically conductive material, such as metal, and thus have electrically conductive properties. The cover 67 may shield electrically non-conductive members, such as the electrically insulating member 65, from charged particles emitted from plasma generated in the plasma generation region 25 (see FIG. 2).

Referring to FIG. 3, the shield electrode 68 may be fixed to an inner wall of the cover 67 through a ring 69 having electrically non-conductive properties. The shield electrode 68 may have a through-hole 68 f formed therein to allow targets 27 to pass therethrough.

The target controller 52 may be configured to output control signals respectively to the pressure adjuster 53, the DC power supply 55, the pulse voltage power supply 58, and the DC power supply 59. The inert gas cylinder 54 may be connected to the pressure adjuster 53 through a pipe. Further, the pressure adjuster 53 may be in communication with the interior of the reservoir 61 through another pipe.

An output terminal of the DC power supply 55 may be electrically connected to an electrode 63 provided inside the reservoir 61 through a feedthrough 57 a provided in the reservoir 61. The electrode 63 may be in contact with the target material stored in the reservoir 61. When the reservoir 61 is formed of an electrically conductive material, the output terminal of the DC power supply 55 may be electrically connected to the reservoir 61, and the feedthrough 57 a does not need to be provided.

An output terminal of the pulse voltage power supply 58 may be electrically connected to the pull-out electrode 66 through a feedthrough 58 a provided in the flange 84 and a through-hole 65 a provided in the electrically insulating member 65. An output terminal of the DC power supply 59 may be electrically connected to the shield electrode 68 through a feedthrough 59 a provided in the flange 84.

With reference to FIG. 2 again, a beam steering unit 34 a and the EUV light generation controller 5 may be provided outside the chamber 2. The beam steering unit 34 a may include high-reflection mirrors 341 and 342 and holders 343 and 344 for holding the high-reflection mirrors 341 and 342, respectively.

3.2 Operation

Referring to FIG. 3, the pressure adjuster 53 may be configured to adjust a pressure of an inert gas supplied from the inert gas cylinder 54 and pressurize the molten target material inside the reservoir 61 by the inert gas in accordance with a control signal from the target controller 52. As the target material is pressurized by the inert gas, the target material may protrude slightly from the protrusion 62 b through the through-hole formed in the nozzle plate 62.

The DC power supply 55 may apply a potential P3 to the target material in the reservoir 61 through the electrode 63 in accordance with a control signal from the target controller 52. The pulse voltage power supply 58 may apply a pulsed potential P7 to the pull-out electrode 66 in accordance with a control signal from the target controller 52. Thus, an electric field may be generated between the target material and the pull-out electrode 66, and the Coulomb force may act between the target material and the pull-out electrode 66.

The electric field may be enhanced particularly around the target material protruding from the protrusion 62 b, and thus, the Coulomb force may be enhanced between the target material protruding from the protrusion 62 b and the pull-out electrode 66. Accordingly, _(the) target 27 may be outputted from the protrusion 62 b in the form of a charged droplet.

Referring to FIG. 3, the cover 67 and the wall of the chamber 2 may be electrically connected to a constant potential Pl. The constant potential P1 may be the ground potential of 0 V. The DC power supply 59 may apply a potential P2 to the shield electrode 68.

Referring to FIG. 2, the target controller 52 may be configured to control the pressure adjuster 53 and the pulse voltage power supply 58 such that the target 27 is outputted at a timing specified by the EUV light generation controller 5. The outputted target 27 may be supplied to the plasma generation region 25 in the chamber 2.

Referring to FIG. 2, a pulse laser beam outputted from the laser apparatus 3 may be reflected by the high-reflection mirrors 341 and 342, and may enter the laser beam focusing optical system 22 a through the window 21. The pulse laser beam that has entered the laser beam focusing optical system 22 a may be reflected by the off-axis paraboloidal mirror 221 and the flat mirror 222. The EUV light generation controller 5 may control various components so that the target 27 outputted from the target supply device 26 is irradiated with the pulse laser beam at a timing when the target 27 reaches the plasma generation region 25.

FIGS. 4A and 4B are diagrams showing examples of potentials to be applied to various components in a target supply device. The DC power supply 55 (see FIG. 3) may retain the potential P3 of the target material in the reservoir 61 at a predetermined potential Phv, for example, of 20 kV. The pulse voltage power supply 58 may first retain the potential P7 of the pull-out electrode 66 at a potential P_(H), for example, of 15 kV, and change the potential P7 to a potential P_(L), for example, of 5 kV when a target 27 is to be outputted. Then, the pulse voltage power supply 58 may change the potential P7 back to the potential P_(H) after a predetermined time ΔT7 elapses. Here, the potential P_(H) and the potential P_(L) may fall within a range of Phv≧P_(H)>P_(L)≧P1. The potential P1 may be the same as the potential of the cover 67 and the chamber 2, which may be the ground potential.

After a target 27 is outputted, the target 27 may reach the plasma generation region 25 and be irradiated with a pulse laser beam, and thus, plasma may be generated. If charged particles included in the plasma reach the nozzle plate 62 of the target supply device 26, or the vicinity thereof, the potential P3 of the target material and the potential P2 of the shield electrode 68 may temporarily change as shown in FIG. 4A. In that case, even if the potential P7 of the pull-out electrode 66 is controlled in order to generate a subsequent target 27, a potential difference between the potential P3 of the target material and the potential P7 of the pull-out electrode 66 may not be controlled to a desired potential difference. Accordingly, the speed and/or the trajectory of the subsequent target 27 may vary.

Here, as shown in FIG. 4B, when the potential P2 of the shield electrode 68 is controlled to a potential that is lower than the potential P1 of the cover 67, a change in the potential P3 of the target material may be suppressed.

FIG. 4C is a graph showing an amount of change in the potential of the shield electrode and the potential of the target material after plasma generation with respect to a potential of the shield electrode. Due to the influence by charged particles emitted from the plasma, the potential P3 of the target material and the potential P2 of the shield electrode 68 may change after plasma generation. The maximum value of an amount of change in the potential P3 in this case is designated as ΔP3, and the maximum value of an amount of change in the potential P2 is designated as ΔP2 (see FIG. 4A). FIG. 4C shows obtained data in the case where the repetition rate of plasma generation was set to 10 Hz and the diameter of the through-hole 68 f in the shield electrode 68 was set to 3 mm.

As shown in FIG. 4C, when the potential P2 of the shield electrode 68 was positive, an amount of change or decrease ΔP3 in the potential P3 of the target material was in the range of 800 V to 1200 V, and an amount of change or decrease ΔP2 in the potential P2 of the shield electrode 68 was in the range of 0 V to 120 V. On the other hand, when the potential P2 of the shield electrode 68 is a negative potential that is equal to or lower than −500 V, the potential P3 of the target material and the potential P2 of the shield electrode 68 did not change essentially after plasma generation.

When the repetition rate of plasma generation is set higher than 10 Hz, a larger number of charged particles may be generated inside the chamber 2, and thus, the potential P2 of the shield electrode 68 may desirably be set to an even lower negative potential. For example, when the repetition rate of plasma generation is set to 1 kHz, it is desirable to set the potential P2 of the shield electrode 68 to equal to or lower than −800 V. Then, a change in the potential P3 of the target material after plasma generation may be suppressed. Thus, a potential difference between the potential P3 of the target material and the potential P7 of the pull-out electrode 66 may be controlled to a desired potential difference, and a variation in the speed and/or the trajectory of the targets 27 may be suppressed.

3.3 Examples of Shield Electrode

FIG. 5A is a plan view illustrating an example of a shield electrode used in the target supply device of the first embodiment. FIG. 5B is a sectional view illustrating the shield electrode shown in FIG. 5A being attached to the cover 67.

The shield electrode shown in FIGS. 5A and 5B may include a ring 68 a having electrically conductive properties and a mesh 68 b having electrically conductive properties. The ring 68 a and the mesh 68 b may be formed of metal. The ring 68 a may be fixed to the mesh 68 b. The mesh 68 b may be affixed to a sheet 69 a having electrically non-conductive properties. The sheet 69 a may have a through-hole 69 b formed therein. The sheet 69 a may be fixed to the ring 69, and the ring 69 may be fixed to the cover 67. With this configuration, the ring 68 a and the mesh 68 b may be positioned at a predetermined distance from the cover 67. A space 68 c at the center of the mesh 68 b, the through-hole 69 b in the sheet 69 a, and the through-hole 67 a in the cover 67 may be aligned linearly along the designed trajectory of the target 27.

The target 27 outputted from the target supply device 26 may pass through the space 68 c at the center of the mesh 68 b, the through-hole 69 b in the sheet 69 a, and the through-hole 67 a in the cover 67. The size of the space 68 c may preferably be small but large enough not to interfere with passage of the target 27. For example, the dimension of the space 68 c may be larger than the largest cross-section of the target 27 and equal to or smaller than 3 mm. In one embodiment, the dimension may be equal to or smaller than 2 mm, or in another embodiment, the dimension may be equal to or smaller than 1 mm. Then, charged particles may be prevented from reaching the nozzle plate 62 of the target supply device 26, or the vicinity thereof. Accordingly, a change in the potential P3 of the target material may be suppressed.

FIG. 6A is a plan view illustrating another example of a shield electrode used in the target supply device of the first embodiment. FIG. 6B is a sectional view illustrating the shield electrode shown in FIG. 6A being attached to a cover.

The shield electrode 68 shown in FIGS. 6A and 6B may include a plate 68 d having electrically conductive properties, in place of the mesh 68 b (see FIGS. 5A and 5B). The plate 68 d may be formed of metal. The plate 68 d may have a through-hole 68 e formed therein. The ring 68 a may be fixed to the plate 68 b. The plate 68 a may be affixed to the sheet 69 a.

The size of the through-hole 68 e may preferably be small but large enough not to interfere with passage of the target 27. Other configurations may be similar to those described with reference to FIGS. 5A and 5B.

4. Target Supply Device Including Acceleration Electrode

FIG. 7 is a partial sectional view illustrating a target supply device according to a second embodiment of the present disclosure and peripheral components thereof. In the second embodiment, the shield electrode 68 may be fixed to the outer wall of the cover 67 through the ring 69. Further, an acceleration electrode 64 may be provided downstream from the pull-out electrode 66 in the direction in which the target 27 travels. The acceleration electrode 64 may be held in the electrically insulating member 65.

As described in the first embodiment, the DC power supply 55 may retain the potential P3 of the target material in the reservoir 61 at a predetermined potential Phv, for example, of 20 kV. The pulse voltage power supply 58 may first retain the potential P7 of the pull-out electrode 66 at a potential P_(H), for example, of 15 kV, and change the potential P7 to a potential P_(L), for example, of 5 kV when a target 27 is to be outputted. Then, the pulse voltage power supply 58 may change the potential P7 back to the potential P_(H) after a predetermined time ΔT7 elapses. Here, the potential P_(H) and the potential P_(L) may fall within a range of Phv≧P_(H)>P_(L)>P1. The potential P1 may be the same as the potential of the cover 67 and the chamber 2, which may be the ground potential.

With the above-described operations, a positively charged target 27 may be outputted through the nozzle plate 62. The target 27 may travel toward the pull-out electrode 66 to which the potential P7 that is lower than the potential P3 of the target material is applied, and may pass through the through-hole 66 a in the pull-out electrode 66.

The acceleration electrode 64 may be electrically connected to the potential P1, which is, for example, the ground potential. Then, the positively charged target 27 that has passed through the through-hole 66 a may be accelerated toward the acceleration electrode 64.

In this way, the target 27 may be accelerated through a potential gradient formed along the designed trajectory from the nozzle plate 62 to the acceleration electrode 64 through the pull-out electrode 66, and may pass through a through-hole 64 a formed in the acceleration electrode 64. The potential gradient along the path of the target 27 that has passed through the through-hole 64 a may be gradual since the potential of the cover 67 and the chamber 2 is the ground potential, which is the same as the potential of the acceleration electrode 64. Accordingly, after passing through the through-hole 64 a, the target 27 may travel inside the chamber 2 primarily with its kinetic momentum at the time of passing through the through-hole 64 a.

The DC power supply 59 may apply the potential P2 to the shield electrode 68. The potential P2 of the shield electrode 68 may be controlled to a potential that is lower than the potential P1 of the cover 67. Even in this case, charged particles may be prevented from reaching the nozzle plate 62 of the target supply device 26, or the vicinity thereof. Accordingly, a potential difference between the potential P3 of the target material and the potential P7 of the pull-out electrode 66 may be controlled to a desired potential difference.

In the second embodiment as well, since a potential difference between the potential P3 of the target material and the potential P7 of the pull-out electrode 66 can be controlled to a desired potential difference, a variation in charge given to a target 27 may be suppressed. Accordingly, a variation in the speed of the target 27 accelerated by the acceleration electrode 64 may be suppressed. Further, by controlling the potential P2 of the shield electrode 68 to a potential that is lower than the potential P1 of the cover 67, charged particles may be prevented from reaching the acceleration electrode 64 or the vicinity thereof. Accordingly, the potential of the acceleration electrode 64 may be stabilized, and hence a variation in the speed of the target 27 accelerated by the acceleration electrode 64 may be suppressed. The acceleration electrode 64 may also be provided in the target supply device 26 according to the first embodiment.

5. Target Supply Device Including Cover for Shielding Reservoir 5.1 Configuration

FIG. 8 is a partial sectional view illustrating a target supply device according to a third embodiment of the present disclosure and peripheral components thereof. In the third embodiment, a cover 85 may cover the reservoir 61, the nozzle plate 62, the electrically insulating member 65, and the pull-out electrode 66. The cover 85 may further cover the acceleration electrode 64 and deflection electrodes 70 which will be described later.

As shown in FIG. 8, primary components of the target supply device 26 may be housed in a shielding container formed by the cover 85 and a lid 86 attached to cover an opening in the cover 85. The cover 85 may be mounted to the wall of the chamber 2. The cover 85 may have a through-hole 85 a formed therein to allow targets 27 to pass therethrough. The lid 86 may airtightly seal the opening in the cover 85 located outside of the chamber 2. The reservoir 61 may be attached to the lid 86.

The cover 85 may be formed of an electrically conductive material, such as metal, and thus may have electrically conductive properties. The cover 85 may be electrically connected to the wall of the chamber 2 either directly or through an electrically conducive connection member, such as a wire. The wall of the chamber 2 may be electrically connected to the ground potential. The lid 86 may be formed of an electrically non-conductive material, such as mullite. The cover 85 may be provided to shield electrically non-conductive materials, such as the electrically insulating member 65, from charged particles emitted from plasma generated in the plasma generation region 25.

A plurality of deflection electrodes 70 may be provided downstream from the acceleration electrode 64 in the direction in which the target 27 travels. In the example shown in FIG. 8, two pairs of deflection electrodes 70 may be provided. Each of the deflection electrodes 70 may be held by the electrically insulating member 65 in an electrically insulated state.

Wiring of the shield electrode 68 and wiring of the deflection electrodes 70 may be electrically connected respectively to the DC power supply 59 and a deflection electrode power supply 57 through a relay terminal 90 a provided in the lid 86. The wiring of the deflection electrodes 70 may pass through a through-hole formed in the electrically insulating member 65. Wiring of the acceleration electrode 64 may be electrically connected to the cover 85 through another through-hole formed in the electrically insulating member 65.

Wiring of the electrode 63 may be electrically connected to the DC power supply 55 through a relay terminal 90 b provided in the lid 86. Wiring of the pull-out electrode 66 may be electrically connected to the pulse voltage power supply 58 through yet another through-hole formed in the electrically insulating member 65 and a relay terminal 90 c provided in the lid 86.

Although not shown in FIG. 8, an inert gas cylinder may be connected to the pressure adjuster 53 through a pipe, as in the first and second embodiments.

5.2 Operation

The target controller 52 may be configured to output control signals respectively to the pressure adjuster 53, the DC power supply 55, the deflection electrode power supply 57, and the pulse voltage power supply 58. Then, a charged target 27 may be outputted through the nozzle plate 62, and may pass through the through-hole 66 a in the pull-out electrode 66. The target 27 that has passed through the through-hole 66 a may be accelerated through an electric field between the pull-out electrode 66 and the acceleration electrode 64 to which the ground potential is applied, and may pass through the through-hole 64 a in the acceleration electrode 64.

The two pairs of deflection electrodes 70 may cause an electric field to act on the charged target 27 that has passed through the through-hole 64 a to deflect its traveling direction. When the target 27 needs to be deflected, the target controller 52 may output a control signal to the deflection electrode power supply 57 to control a potential difference between each pair of the deflection electrodes 70. The deflection electrode power supply 57 may be configured to apply a voltage between each pair of the deflection electrodes 70.

The target 27 may be deflected based on a control signal from the EUV light generation controller 5 (see FIG. 2). Various signals may be transmitted between the EUV light generation controller 5 and the target controller 52. For example, the EUV light generation controller 5 may obtain information on the trajectory of the target 27 from a target sensor (not separately shown), and calculate a difference between the obtained trajectory and an ideal trajectory. Further, the EUV light generation controller 5 may send a signal to the target controller 52 to control a voltage applied between each pair of the deflection electrodes 70 so that the aforementioned difference is reduced. Here, the target 27 that has passed through the two pairs of the deflection electrode 70 may pass through the through-hole 85 a in the cover 85.

FIG. 9 is a diagram for illustrating a method for controlling a direction of a target using the deflection electrodes. Described below is a case where a charged target 27 traveling in the Z-direction is deflected in the X-direction through an electric field using a pair of flat electrodes 70 a and 70 b serving as deflection electrodes.

A charged target 27 having a charge Q may be subjected to the Coulomb force F expressed in the following expression through an electric field E between the flat electrodes 70 a and 70 b. Here, the description to follow is based on the assumption that the electric lines of force between the flat electrodes 70 a and 70 b are substantially parallel to one another anywhere between the flat electrodes 70 a and 70 b.

F=QE

The electric field E may be expressed in the following expression by a potential difference (Pa−Pb) between a potential Pa given to the flat electrode 70 a and a potential Pb given to the flat electrode 70 b and a length G between the flat electrodes 70 a and 70 b.

E=(Pa−Pb)/G

When a target 27 enters the electric field E with an initial speed V_(O), the target 27 may be subjected to the Coulomb force F in a direction orthogonal to its travel direction. Thus, the target 27 may be deflected. Accordingly, the target 27 may be accelerated in the X-direction by the Coulomb force F while moving in the Z-direction with a Z-direction velocity component V_(z) (V_(z)=V_(O)). The target 27 may be subjected to the Coulomb force F while the target 27 is in the electric field E. Acceleration a in the Z-direction at this time may be obtained from the expression below when mass m of the target 27 is known.

F=ma

Further, an X-direction velocity component V_(x) at a time when the target 27 exits the electric field E may be induced through the following expression.

V _(x) =aL/V _(z) (L: length of the electrode 70 in the Z-direction)

The speed V of the target 27 at the time when the target 27 exits the electric field E may be expressed in the following expression by the Z-direction velocity component V_(z) and the X-direction velocity component V_(x).

V=(V _(z) ² +V _(x) ²)^(1/2)

In this way, the target 27 may be deflected by providing a potential difference (Pa−Pb) to cause an electric field to act on a part of the trajectory of the target 27. Further, adjusting the potential difference (Pa−Pb) may make it possible to control the deflection amount. The target 27 that has exited the electric field may travel at the speed V and arrive at a position in a laser beam path, at which the target 27 may be irradiated with a pulse laser beam. Similarly, the target 27 may be deflected in the Y-direction through an electric field generated between a pair of flat electrodes arranged in the Y-direction.

In the third embodiment as well, charged particles may be prevented from reaching the nozzle plate 62 of the target supply device 26, or the vicinity thereof by applying the potential P2 to the shield electrode 68. Accordingly, a potential difference between the potential P3 of the target material and the potential P7 of the pull-out electrode 66 may be controlled to a desired potential difference.

Further, since a potential difference between the potential P3 of the target material and the potential P7 of the pull-out electrode 66 can be controlled to a desired potential difference, a variation in a charge given to the target 27 may be suppressed. Accordingly, the trajectory of the target 27 may be controlled to a desired trajectory. Furthermore, by controlling the potential P2 of the shield electrode 68 to a potential that is lower than the potential P1 of the cover 85, charged particles may be prevented from reaching the deflection electrodes 70 or the vicinity thereof. Accordingly, the potential of the deflection electrodes 70 may be controlled to a desired potential, and the trajectory of the target 27 may be controlled to a desired trajectory. The deflection electrodes 70 may also be provided in the target supply device 26 of the first or second embodiment.

6. Target Supply Device Where Pulse Voltage is Applied to Shield Electrode

FIG. 10 is a partial sectional view illustrating an exemplary configuration of an EUV light generation system including a target supply device according to a fourth embodiment of the present disclosure. In the fourth embodiment, in place of the DC power supply 59 (see FIG. 2), a pulse power supply 59 b may be electrically connected to the shield electrode 68. The pulse power supply 59 b may be configured to apply a pulsed potential to the shield electrode 68.

FIG. 11 is a diagram showing an example of potentials applied to various components in the target supply device of the fourth embodiment. As shown in FIG. 11, the pulse power supply 59 b may raise the potential P2 of the shield electrode 68 to a predetermined potential around the ground potential for a time period from a time at which a target 27 is generated to a time at which the target 27 has passed through the through-hole 67 a in the cover 67, and may retain the potential P2 at a negative potential that is lower than the aforementioned predetermined potential during the remaining time period. Plasma may be generated after the potential P2 of the shield electrode 68 is lowered from the aforementioned predetermined potential back to a negative potential that is lower than the aforementioned predetermined potential.

When a trigger signal is outputted to the pulse voltage power supply 58 from the target controller 52, a trigger signal may also be outputted to the pulse power supply 59 b from the target controller 52. Accordingly, when a pulse voltage is applied to the pull-out electrode 66 by the pulse voltage power supply 58, a pulse voltage may also be applied to the shield electrode 68 by the pulse power supply 59 b. A pulse duration ΔT2 of the pulse voltage applied to the shield electrode 68 may be at least in duration from a time at which a target 27 is generated to a time at which the target 27 has passed through the through-hole 67 a in the cover 67.

With the above-described configuration, the potential gradient between the shield electrode 68 and the cover 67 may be reduced until a target 27 passes through the shield electrode 68 and the cover 67, and acceleration/deceleration of the target 27 in the vicinity of the shield electrode 68 may be suppressed. After the target 27 passes through the shield electrode 68 and the cover 67, the potential P2 of the shield electrode 68 may be controlled to a predetermined negative potential, and thus, charged particles emitted from the plasma may be prevented from reaching the nozzle plate 62 of the target supply device 26, or the vicinity thereof. Accordingly, a potential difference between the potential P3 of the target material and the potential P7 of the pull-out electrode 66 may be controlled to a desired potential difference, and a variation in the speed and/or the trajectory of the target 27 may be suppressed.

7. Variations of Target Supply Device

FIG. 12 is a sectional view illustrating a part of a target supply device according to a fifth embodiment of the present disclosure. In the fifth embodiment, a nozzle pipe 74 may be connected to a reservoir (not separately shown). A piezoelectric ceramic element, such as a lead zirconate titanate (PZT) element 76, may be fixed to the nozzle pipe 74. A PZT driving power supply 77 may be electrically connected to the PZT element 76. The PZT driving power supply 77 may be connected to the target controller 52 through a signal line. Further, the pressure adjuster 53 (see FIG. 3) described in the first embodiment may pressurize a liquid target material in the reservoir.

The target controller 52 may send a control signal to the PZT driving power supply 77 in accordance with a signal from the EUV light generation controller 5. The PZT driving power supply 77 may apply a driving voltage to the PZT element 76 in accordance with the received control signal.

The target material may be outputted on-demand in the form of droplets through an opening 74 a through a method in which a driving voltage is applied to the PZT element 76 to cause the nozzle pipe 74 to deform at a predetermined timing. Alternatively, a continuous jet of the target material may be generated by pressurizing the target material in the reservoir by the pressure adjuster 53 described in the first embodiment, and the jet of the target material may be divided into droplets by vibration of the PZT element 76 to which a driving voltage is applied.

In the fifth embodiment as well, the nozzle pipe 74 may be covered by the cover 67 having the through-hole 67 a formed therein to allow targets 27 to pass therethrough. The shield electrode 68 having the through-hole 68 f formed therein may be fixed to the cover 67 through the ring 69. A potential of the cover 67 may be controlled to the ground potential, and the potential P2 of the shield electrode 68 may be controlled to a potential that is lower than the potential of the cover 67.

In this way, charged particles may be prevented from reaching the nozzle pipe 74 of the target supply device, or the vicinity thereof. Accordingly, charged particles may be prevented from adhering to the periphery of the opening 74 a in the nozzle pipe 74. Thus, the wettability of the periphery of the opening 74 a may be prevented from being changed. As a result, a variation in the trajectory of the target 27 may be suppressed.

The above-described embodiments and the modifications thereof are merely examples for implementing the present disclosure, and the present disclosure is not limited thereto. Making various modifications according to the specifications or the like is within the scope of the present disclosure, and other various embodiments are possible within the scope of the present disclosure. For example, the modifications illustrated for particular ones of the embodiments can be applied to other embodiments as well (including the other embodiments described herein).

The terms used in this specification and the appended claims should be interpreted as “non-limiting.” For example, the terms “include” and “be included” should be interpreted as “including the stated elements but not limited to the stated elements.” The term “have” should be interpreted as “having the stated elements but not limited to the stated elements.” Further, the modifier “one (a/an)” should be interpreted as “at least one” or “one or more.” 

What is claimed is:
 1. A target supply device, comprising: a nozzle portion having a through-hole defined therein to allow a target material to be discharged therethrough; a cover including an electrically conductive material and disposed to cover the nozzle portion, the cover having a through-hole defined therein to allow the target material to pass therethrough; a first electrode disposed on the cover, the first electrode having a through-hole to allow the target material to pass therethrough; and a potential controller configured to control the first electrode to have a first potential that is lower than a second potential of the cover.
 2. The target supply device according to claim 1, further comprising a second electrode facing the nozzle portion, wherein the potential controller is configured to: control the target material to have a third potential that is higher than the first potential, and vary in pulses a potential of the second electrode between a fourth potential that is higher than the second potential and equal to or lower than the third potential, and a fifth potential that is equal to or higher than the second potential and lower than the fourth potential.
 3. The target supply device according to claim 2, wherein the potential controller is configured to control the first electrode to have a sixth potential that is higher than the first potential for a predetermined time after the target material is outputted from the nozzle portion and thereafter control the first electrode to have the first potential.
 4. The target supply device according to claim 3, wherein a difference between the sixth potential and the second potential is smaller than a difference between the sixth potential and the first potential.
 5. The target supply device according to claim 1, wherein the first electrode is disposed on an inner wall of the cover.
 6. The target supply device according to claim 1, wherein the first electrode is disposed on an outer wall of the cover. 